The purpose of this study is to assess and compare the safety and effectiveness of CholestaGel (colesevelam hydrochloride), an experimental medication for lowering high blood cholesterol levels, in combination with simvastatin. CholestaGel is investigational and may help in the treatment of hypercholesterolemia (high levels of cholesterol in the blood). High levels of cholesterol in the blood can lead to atheroscelorsis (hardening of the arteries), causing heart attacks or stroke. Simvastatin has previously been proven to effectively lower cholesterol levels, and has been available in the U.S. since 1991, when it was approved by the FDA.